Conservation of angular momentum

When a figure skater pulls their arms in close to their body, they decrease their moment of inertia. Because angular momentum must remain constant in a closed system, their rotational speed dramatically increases to compensate.

Gyroscopes remain upright due to the conservation of angular momentum, as their rapidly spinning wheel creates a powerful resistance to external torques. The angular momentum vector resists changing direction, allowing the gyroscope to balance perfectly on a tiny pivot.

Yes, in a closed system where no external torque is applied, the total angular momentum remains perfectly constant. This is a fundamental law of physics that governs everything from planetary orbits to subatomic particles.

A falling cat manipulates its body shape—bending at the waist and extending or retracting its legs—to change its moment of inertia. Even though the cat has zero initial angular momentum, this internal body manipulation allows it to twist and land upright.